Can't use system installed gRPC

[nfrmtk]

Relates: #255 Right now error is following:

  By not providing "Findgrpc.cmake" in CMAKE_MODULE_PATH this project has
  asked CMake to find a package configuration file provided by "grpc", but
  CMake did not find one.

  Could not find a package configuration file provided by "grpc" with any of
  the following names:

    grpcConfig.cmake
    grpc-config.cmake

  Add the installation prefix of "grpc" to CMAKE_PREFIX_PATH or set
  "grpc_DIR" to a directory containing one of the above files.  If "grpc"
  provides a separate development package or SDK, be sure it has been
  installed.